leaflet tutorial

library

library(leaflet)
library(dplyr)
library(RColorBrewer)
library(sf)

Basic map and markers

leaflet() |>
  addTiles() |>
  setView(lng = 121.774, lat = 12.8797, zoom = 6) |>
  addMarkers(lng = 120.9842, lat = 14.5995, popup = "Manila") |>
  addMarkers(lng = 125.5017, lat = 8.4753, popup = "Butuan City") |> 
  addMarkers(lat = 15.671818823094426, lng = 120.89067531956579, popup = "PhilRice")

🧠 Exercise 1:

Add a marker for your house and the house of you

• Add popups with city names

• Try adjusting the zoom level

2. 🌟 Customizing Markers

Demo

customIcon <- makeIcon(
  iconUrl ="https://raw.githubusercontent.com/nmfrancisco14/phl_maps/master/DAC - LOGO OFFICIAL.png",
  iconWidth = 100,
  iconHeight = 100 )


leaflet() |>   
  addTiles() |>
  setView(lng = 121.774, lat = 12.8797, zoom = 6) |>
  addMarkers(lat = 15.671818823094426, 
             lng = 120.89067531956579, 
             icon = customIcon, popup = "Data Analytics Center") 

🧠 Exercise 2:

Use a different PNG icon (e.g. from Wikimedia or GitHub) and place it in Cebu or Davao.

• What happens if you change the icon size?

• Try using different shapes or logos.

3. 🧭 Polygons & Polylines

Load boundaries:

ph_province <- st_read(
  "https://raw.githubusercontent.com/nmfrancisco14/phl_maps/master/phl_provinces_ncr-districts_icc.geojson")

Reading layer `phl_provinces_ncr-districts_icc' from data source 
  `https://raw.githubusercontent.com/nmfrancisco14/phl_maps/master/phl_provinces_ncr-districts_icc.geojson' 
  using driver `GeoJSON'
Simple feature collection with 88 features and 5 fields
Geometry type: MULTIPOLYGON
Dimension:     XY
Bounding box:  xmin: 116.9283 ymin: 4.58694 xmax: 126.6053 ymax: 21.07014
Geodetic CRS:  WGS 84

Demo: Add polygon boundaries

leaflet(ph_province) |>
  addTiles() |>
  addPolygons(fillColor = "lightblue", 
              fillOpacity = 0.5, 
              color = "black", 
              weight = 1) 

Demo: Draw a path

coords <- data.frame(   
  lng = c(120.9842, 121.7740, 122.5644),   
  lat = c(14.5995, 12.8797, 11.0046) )


leaflet() |>   
  addTiles() |>   
  addPolylines(data = coords, 
               lng = ~lng, 
               lat = ~lat, 
               color = "red", 
               weight = 2) 

🧠 Exercise 3:

• Modify the polygon fill color.

• Create a polyline connecting Cebu → Tacloban → Davao.

4. 🔵 Circles

Demo:

leaflet() |>
  addTiles() |>
  setView(lng = 121.774, lat = 12.8797, zoom = 6) |>
  addCircles(lng = 121.774, 
             lat = 12.8797, 
             radius = 50000,
             color = "blue", 
             fillColor = "blue", 
             fillOpacity = 0.5,              
             popup = "Central PH") 

🧠 Exercise 4:

Add a circle around Davao with a 30km radius. Try different fillOpacity and popup text.

5. 💬 Popups & Labels

Demo:

leaflet() |>   
  setView(lng = 121.774, lat = 12.8797, zoom = 6) |>
  addTiles() |>   
  addMarkers(     
    lng = 123.8854, 
    lat = 10.3157,     
    popup = "<b>Cebu City</b><br>Queen City of the South",
    label = "Hover for label") 

🧠 Exercise 5:

Add a marker for Vigan with:

• Bold popup text

• Label text with italics

6. 🗺️ Basemaps & Layers

Demo:

# lists
browseURL("https://leaflet-extras.github.io/leaflet-providers/preview/")

leaflet() |>   
  addProviderTiles("CartoDB.Positron") |>   
  addProviderTiles("OpenStreetMap.Mapnik", group = "MapNik") |> 
  addProviderTiles("Esri.WorldImagery", group = "Satellite") |>   
  addLayersControl(baseGroups = c("CartoDB.Positron", "MapNik","Satellite"),     
                   options = layersControlOptions(collapsed = FALSE)   ) |>
  setView(lat = 12.8797, lng = 121.7740, zoom = 6) 

🧠 Exercise 6:

• Add a new tile layer:

• Add 3 base layers, and test switching views

7. 🏷️ Legends

Demo: Categorical

phl_data <-  read.csv("https://raw.githubusercontent.com/nmfrancisco14/phl_maps/master/phl_data.csv")


ph_mapdata <- 
  ph_province |> 
  left_join(phl_data |> 
              select(islandGroup,province=location,Production:SuffRatio))

Joining with `by = join_by(province)`

colors <- colorFactor(c("darkgreen", "orange", "blue"), 
                      domain = c("Luzon", "Visayas", "Mindanao"))



leaflet(ph_mapdata) |>   
  addTiles() |>   
  addPolygons(fillColor = ~colors(islandGroup), 
              fillOpacity = 0.6, color = "white") |>   
  addLegend("bottomright", 
            pal = colors, 
            values = ~islandGroup, 
             title = "Island Group") 

🧠 Exercise 7:

• Change the colors in colorFactor() (e.g., use "red", "yellow", "green")

• Try positioning the legend at "topright"

8. 🌡️ Choropleth Mapping

Demo: Numeric variable

#| echo: true



pal <- colorNumeric("YlOrRd", domain = ph_mapdata$population)  

leaflet(ph_mapdata) |>   
  addTiles() |>   
  addPolygons(fillColor = ~pal(population), 
              weight = 1,               
              fillOpacity = 0.7, color = "white",               
              popup = ~paste0(province, ": ", format(population, big.mark=","))) |>   
  addLegend("bottomright", 
            pal = pal, 
            values = ~population,             
            title = "Population") 

🧠 Exercise 8:

• Map new numeric variable it using a new color palette like "Greens" or "PuBu"

✅ Wrap-Up & Practice Ideas

🎯 Challenges:

• Create a choropleth map showing yield groups

• Create a map highlighting the top 10 and bottom 10 on production, area , yield and sufficiency ratio

💾 Save Your Map:

library(htmlwidgets) 

map <- leaflet(ph_mapdata) |>   
  addTiles() |>   
  addPolygons(fillColor = ~pal(population), 
              weight = 1,               
              fillOpacity = 0.7, color = "white",               
              popup = ~paste0(province, ": ", format(population, big.mark=","))) |>   
  addLegend("bottomright", 
            pal = pal, 
            values = ~population,             
            title = "Population") 

saveWidget(widget =map , file = "my_leaflet_map.html")